The present invention is drawn to thermally and structurally stable noncombustible papers and methods of making the same.
In recent years, there has been an increased demand for lightweight sheet-like products that are fire retardant, or even noncombustible. This is particularly true after the health hazards of such materials such as asbestos have become known. Aside from the health risks associated with asbestos, asbestos was a good product for several reasons including its ability to conform with water during the paper making process. Additionally, asbestos products have shown good adsorptivity and scavenging properties in mixing with other additives.
Because asbestos has been restricted in recent years due to certain health concerns, alternative fibrous products having similar properties have become of interest. For example, highly efficient inorganic fibers have been developed including plaster fibers, basic magnesium sulfate fibers, phosphoric acid fibers, pyroboric acid magnesium fibers, potassium titanate fibers, alumina-silica fibers, and glass fibers, to name a few. Additionally, some fire retardant products have been developed including products focused on the coating of papers with an anti-flaming agent. Such anti-flaming agents have included ammonium salt complex type aqueous inorganic salts, phosphorus complex nitrogen compounds, phosphorus complex hologen compounds, antimonytrioxide-halogen compounds, boron compounds, halogen compounds, and the like. These coating systems are typically composed of organic substances, and because they are mere coatings, it is very difficult to form a sheet-like material that is totally noncombustible.
Therefore, based upon what is known about the prior art, it has been recognized that a fibrous paper product that is structurally stable at very high temperature, such as when in contact with a flame, would be a significant advancement in the paper insulation art.
The present invention is drawn to a noncombustible fibrous paper comprising a dominant amount of aluminosilicate refractory fibers by weight, wherein the fibers are substantially from 1 micron to 35 microns in width and from 1 cm to 15 cm in length; and from 0.2% to 4% by weight of a polymeric binder distributed throughout the paper. The polymeric binder can be, for example, a vinyl acetate/ethylene copolymer emulsion. The paper is a mat product that is structurally stable at very high temperatures, preferably at temperatures of at least 1000xc2x0 C. and up to 1400xc2x0 C. or more. Though not required, it is preferred that the aluminosilicate refractory fibers be present at from 90% to 99.8% by weight. From 0.1% to 5% by weight of viscose fibers and/or from 0.2% to 5% by weight of silicic acid aquagel, each by weight, can also be present.
Additionally, a method of making a thermally stable noncombustible paper is disclosed comprising the steps of pulping aluminosilicate refractory fibers, adding an effective amount of a polymeric binder forming a continuous pulp, pressing the continuous pulp, and dehydrating the continuous pulp.
Before the present invention is disclosed and described, it is to be understood that this invention is not limited to the particular configurations, process steps and materials disclosed herein as these may vary to some degree. It is also to be understood that the terminology used herein is used for the purpose of describing particular embodiments only, and is not intended to be limiting as the scope of the present invention. The invention will be limited only by the appended claims and equivalents thereof.
It must be noted that, as used in this specification and the appended claims, singular forms of xe2x80x9ca,xe2x80x9d xe2x80x9can,xe2x80x9d and xe2x80x9cthexe2x80x9d include plural referents unless the content clearly dictates otherwise.
xe2x80x9cRefractory fibersxe2x80x9d are fibers that are resistant to heat and corrosion.
xe2x80x9cAluminosilicate refractory fibersxe2x80x9d contain primarily two ingredients: silica (silicon dioxide) and alumina (aluminum dioxide). They are typically present in roughly equal proportions. However, the relative proportions of silica and alumina in the noncombustible paper of the present invention is not critical to the character and quality of the paper, though substantial amounts of both must be present. Thus, as a practical matter, the weight ratio of silica to alumina can be from 7:3 to 3:7. Other trace ingredients can also be present such as  less than 1.0% Fe2O3, and  less than 0.5% Na2O+K2O, though these amounts are not limiting.
xe2x80x9cPaperxe2x80x9d refers to a fibrous product produced by one of a number of paper making processes. Typically, the paper is a compressed mat-type product rather than a woven product. The papers of the present invention are not self-supporting and have many typical paper-like properties, e.g., rollable, foldable, tearable, creasable without breaking, collapseable, bendable, etc. The paper can provide the ability to surround structures of different dimension. In other words, the papers can be collapsible and re-expandable. Additionally, the papers are non-thermally expandable and structurally stable under extreme heat conditions. For example, after applying a 1000xc2x0 C. flame to a paper of the present invention, the paper will not blacken or expand. Thus, until a specific paper reaches a disintegration temperature, e.g. preferably greater than 1000xc2x0 C., it will remain structurally sound.
xe2x80x9cStructurally stablexe2x80x9d or xe2x80x9cthermally stablexe2x80x9d when referring to the papers of the present invention shall mean that the papers will not be significantly physically altered at very high temperatures where direct flame contact with the paper may occur. A very high temperature that can be present in a typical fire can be, for example, at least 230xc2x0 C., though the papers of the present invention can typically withstand much higher temperatures than this. For example, with respect to the preferred embodiments, the papers of the present invention can withstand temperatures of at least 1000xc2x0 C. and up to as much as 1400xc2x0 C. or more, without substantial degradation. Thus, as the paper is structurally stable as defined herein, no substantial expansion or shrinkage, e.g., less than about 3.5% in volume, will occur at very high temperatures, e.g., up to about 1400xc2x0 C. Components other than aluminosilicate refractory fibers can burn off at certain temperatures, e.g., as a gas, though such burn off is not noticeable by casual observation. Thus, in one embodiment, after applying a flame of about 1000xc2x0 C. and allowing the paper cool, the appearance of the paper will remain substantially the same.
xe2x80x9cPaper making processxe2x80x9d is any process wherein the aluminosilicate refractory fibers (with or without other components) are pulped, compressed, and dehydrated.
xe2x80x9cNoncombustiblexe2x80x9d refers to the fact that the papers of the present invention will not substantially combust under extreme heat, but will merely disintegrate into smaller components. For example, many of the papers of the present invention will not disintegrate under a flame of greater than 1000xc2x0 C. However, the papers typically will disintegrate when exposed to an oxy-acetylene torch (2400xc2x0 F.), but will not combust.
xe2x80x9cPolymeric binderxe2x80x9d shall include any polymeric material that is functional in creating binding properties with respect to the aluminosilicate refractory fibers. Though the use of a copolymer emulsion such as vinyl acetate/ethylene is preferred, certain other monomers and copolymers can be used. For example, the polymeric binder can comprise polyvinyl chlorides, polyvinyl acetates, polyvinylidene chlorides, polyvinyl alcohols, polystyrenes, polyethylene terephthalate, polyethylene, polypropylene, polychloroprene, styrene butadiene copolymers, butadiene acrylonitrile copolymers, polyisoprene polyurethanes, polybutadiene, polyacrylates, natural rubbers, silicone, metallic resinates, waxes, acrylic resins, thermoset resins (e.g., epoxies and phenolics), and mixtures and combinations thereof.
xe2x80x9cSecond noncombustible materialxe2x80x9d can include any fibrous material that is noncombustible, such as, for example, glass fibers, glass ceramic fibers, ceramic fibers, mineral fibers, metal fibers, and/or carbon fibers.
The present invention is drawn more specifically to thermally and structurally stable ceramic fiber papers and methods of making these papers. These papers comprise low residue ceramic fibers and are generally formed using wet a paper-making continuous process. With the papers or mat products of the present invention, the momentary reaching temperature can be as high as 1400xc2x0 C. before disintegration occurs. Additionally, working temperatures over 1000xc2x0 C. can be reached without significant degradation or disintegration. At no known temperature will the papers of the present invention combust.
The papers of the present invention exhibit many desirable characteristics in very high temperature environments. For example these papers exhibit low heat conductivity, have low heat melting properties, and have favorable properties with respect to heat-vibration. Additionally, at an appropriate thickness, the papers of the present invention can have very high strength, while maintaining their flexibility. Specifically, by high strength, what is meant is that the papers of the present invention have good initial tear resistance, good tear propagation strength, and good tensile strength. In addition to their low heat conductivity, the added benefits of good electrical and sound insulation are also realized when used in applications where these properties are desirable.
The noncombustible papers of the present invention can be used in many different industries including, but not limited to, the aero industry, the electrical industry, the heat insulation industry, and the automobile industry. For example, heat protection can be provided in the aero industry, heat insulation can be provided for furnaces, and sound insulation can be provided for buildings and automobiles.
Specifically, the noncombustible fibrous papers of the present invention can comprise a dominant amount of aluminosilicate refractory fibers by weight. Typically, this will be from about 90% to 99.8% by weight. Additionally, the fibers used can be substantially from 1 micron to 35 microns in width and from 1 cm to 15 cm in length. Further, the aluminosilicate refractory fibers can comprise from 30% to 70% silica by weight and from 70% to 30% alumina by weight. However, in many instances, the silica and the alumina are present in substantially equal proportions by weight.
As stated, the presence of an effective amount binder must be present in the in order to hold the refractory fibers substantially together in the form of a paper. Anywhere from about 0.2% to 4% by weight of a polymeric binder distributed throughout the paper can be used. The binder can be any carbon-based product that provides strength to the noncombustible paper product. An appropriate polymeric binder that can be used is, for example, a vinyl acetate/ethylene copolymer emulsion. Alternatively, the polymeric binder can comprise any of the following polymers: polyvinyl chlorides, polyvinyl acetates, polyvinylidene chlorides, polyvinyl alcohols, polystyrenes, polyethylene terephthalate, polyethylene, polypropylene, polychloroprene, styrene butadiene copolymers, butadiene acrylonitrile copolymers, polyisoprene polyurethanes, polybutadiene, polyacrylates, natural rubbers, silicone, metallic resinates, waxes, acrylic resins, thermoset resins (e.g., epoxies and phenolics), and mixtures and combinations thereof. If desired, a second polymeric binder can also be added to the pulp prior to dehydration, or can be added as a coating to the compressed pulp (before or after dehydration). In one embodiment, the coating can be a vinyl acetate/ethylene copolymer emulsion, though any of the polymers described previously can also act as the second polymer binder.
Though not required, the paper can also include from 0.1% to 5% by weight of a textile filler. Any known textile filler can be used such as, for example, viscose fiber. Further, the noncombustible paper can also comprise from 0.2% to 5% by weight of silicic acid aquagel. The silicic acid aquagel in the paper of the present invention hardens into roughly spheroid shapes or shots during dehydration of the pulp. The size of the shots in the paper product can be from 40 to 400 microns in width, though this is not critical. In other words, once the silicic acid aquagel is dehydrated during the paper making process, it becomes an amorphous adhesive.
In addition to the silicic acid, incidental amounts of a mineral oxide can be present. For example, a aggregate amount of mineral oxide from about 0.1% to 3% can be present, though this is not important to the present invention. These ingredients can be inherently present in the aluminosilicate refractory fibers, or they can be added separately during the paper making process. Additionally, a second non-combustible material can be used such as, for example, glass fibers, glass ceramic fibers, ceramic fibers, mineral fibers, metal fibers, and/or carbon fibers in effective amounts.
A method of making a noncombustible paper is also disclosed comprising the steps of pulping aluminosilicate refractory fibers, adding an effective amount of a polymeric binder (e.g., vinyl acetate/ethylene copolymer) forming a continuous pulp, pressing the continuous pulp, and dehydrating the continuous pulp. The method produces a mat paper that is structurally stable at very high temperatures such as when in contact with a flame, e.g., up to 1400xc2x0 C.
Optional steps of coating the paper with a polymeric coating can be carried out. The coating can be any polymeric binder such as, for example, a vinyl acetate/ethylene copolymer emulsion. Additionally, the step of adding an effective amount of a textile filler can also be carried out. An effective amount of a viscose fiber can be used for the textile filler. Further, an effective amount of silicic acid aquagel can also be added.
Though not required, the aluminosilicate pulp should be cleaned prior the addition of other ingredients. Additionally, it is preferred that low granule-content aluminosilicate fibers be selected for pulping of the aluminosilicate refractory fibers. Water can also be removed by applying a vacuum to the aluminosilicate-containing pulp. After the aluminosilicate-containing pulp is dehydrated, it can be sized at that point. Prior to pulping, the fibers can be extruded to form textile fibers of having a predetermined dimension. The preferred predetermined dimension can be from 1 micron to 35 microns in width and from 1 cm to 15 cm in length.
Papers prepared in accordance with the principles of the present invention can have many favorable properties. Table 1 below is provided which illustrates some of the target properties that can be achieved with many of the papers of the present invention.
These physical properties and others can vary to some degree, depending on the exact formulation. For example, though any functional thickness can be prepared, from 0.3 mm to 3.0 mm of thickness is preferred. Likewise, any width can be formed, though from 0.3 m to 1.0 m is an appropriate width for a typical paper making machine. Additionally, the weight can be any functional weight, though from 50 to 300 g/m2 is preferred.